Hydrocarbons such as oil and gas are recovered from a subterranean formation using a well or wellbore drilled into the formation. In some cases the wellbore is completed by placing a casing along the wellbore length and perforating the casing adjacent each production zone (hydrocarbon bearing zone) to extract fluids (such as oil and gas) from such a production zone. In other cases, the wellbore may be open hole. One or more flow control devices are placed in the wellbore to control the flow of fluids into the wellbore. These flow control devices and production zones are generally separated from each other by installing a packer between them. Fluid from each production zone entering the wellbore is drawn into a tubing that runs to the surface. It is desirable to have a substantially even flow of fluid along the production zone. Uneven drainage may result in undesirable conditions such as invasion of a gas cone or water cone. In the instance of an oil-producing well, for example, a gas cone may cause an in-flow of gas into the wellbore that could significantly reduce oil production. In like fashion, a water cone may cause an in-flow of water into the oil production flow that reduces the amount and quality of the produced oil.
A deviated or horizontal wellbore is often drilled into a production zone to extract fluid therefrom. Several inflow control devices are placed spaced apart along such a wellbore to drain formation fluid or to inject a fluid into the formation. Formation fluid often contains a layer of oil, a layer of water below the oil and a layer of gas above the oil. For production wells, the horizontal wellbore is typically placed above the water layer. The boundary layers of oil, water and gas may not be even along the entire length of the horizontal well. Also, certain properties of the formation, such as porosity and permeability, may not be the same along the well length. Therefore, fluid between the formation and the wellbore may not flow evenly through the inflow control devices. For production wellbores, it is desirable to have a relatively even flow of the production fluid into the wellbore and also to inhibit the flow of water and gas through each inflow control device. Active flow control devices have been used to control the fluid from the formation into the wellbores. Such devices are relatively expensive and include moving parts, which require maintenance and may not be very reliable over the life of the wellbore. Passive inflow control devices (“ICDs”) that are able to restrict flow of water and gas into the wellbore are therefore desirable.
Horizontal wells for injection and production are used to help maximize the sweep efficiency and economic recovery; especially for recovery of viscous oil in offshore environments. Flow control devices (FCDs) are readily used to control the flow along the well in conventional recovery operations leading to improved recovery efficiency. The benefits of polymer flooding and FCDs has been well demonstrated, however the combination of the two technologies has yet to be fully realized. The cause of FCDs not being as utilized in polymer injection application is due to the severe degradation of the polymer through devices.
Polymer flooding has good potential as an enhanced oil recovery (EOR) option especially for higher conductivity, mature and heavier oil reservoirs. The technique is simply viscosifying the injection water in order to increase the effectiveness of the flooding hence achieving improved sweep efficiency. The polymer is designed in a manner that ensures that the oil phase has a more favourable mobility ratio compared to the pure water injection while working in an injection strategy that has been deemed optimum for the field. Therefore the effectiveness of the polymer flooding strategy is highly dependent on the viscosity of the polymer.
Polymer enhanced oil recovery has been used as an alternative to water flooding to achieve better sweep efficiency; it works by viscosifying the water in order to get a favourable mobility ratio for the oil, hence maintaining the viscosity of the polymer is imperative to the success of the polymer. However as the polymer viscosity increases the frictional effects increase, this becomes much more critical in long horizontal wellbores. Depending on the reservoir quality there may be a significant heel-to-toe effect occurring hence a significant injection flux will occur in the heel and other higher reservoir quality or low pressure environments rather than the entire length of the horizontal wellbore. Hence this impacts the recovery efficiency. Flow control devices and valves can be used to even out the injection flux along the wellbore increasing the recovery efficiency. However the problem with most flow control systems is that it shears the polymer affecting the polymer viscosity. However the present invention illustrates a specific design that can be implemented to significantly minimize the unwanted shearing of the polymer while still providing the equalization of injection flux along the wellbore.
From an economical point of view it is critical that the completion strategy does not adversely impact the polymer quality that would lead to an increase in polymer loading in order to achieve the desired polymer viscosity for the optimum sweep efficiency. Hence the following question emerges: Should Flow Control Devices (FCDs) be utilized when considering that the completion strategy for the injectors should be to eliminate potential nodes that may cause excessively shearing of the polymer? While it has been well understood in the industry that implementation of FCDs can lead to higher recovery efficiency and delaying unwanted fluid breakthrough less is understood about the impact for polymer injectors.
Inflow control devices for production applications are described in U.S. Pat. No. 8,403,038 and shown in some detail in FIGS. 1 and 2. These FIGS. use a velocity profile to illustrate restriction points that cause problems when used for polymer injection where excessive shear alters the polymer viscosity and alters the needed flow rates to achieve the desired production enhancement result from the injection. Other art relating to inflow control devices is US 2009/0205834, U.S. Pat. No. 7,942,206 and U.S. Pat. No. 8,925,633.
FIGS. 1 and 2 show two rotated views of an inflow control device described in U.S. Pat. No. 8,403,038 and designed to perform differently depending on the viscosity of the fluids being produced through it. It features an inlet 10 that leads to spaced inlet passages 12 and 14 that continues into a zig-zag flow regime 16 while moving axially initially in the direction of arrow 18. A direction change occurs at 20 and the zig-zag motion continues as the fluid now travels in the direction of arrow 22 through straight transition passage 24. As seen in FIG. 2 after passage 24 the flow continues in a zig-zag fashion in the direction of arrow 18 to emerge at an outlet 26. Typically after a movement in a circumferential direction clockwise, for example, the flow goes through a small transition passage 30 to continue flowing circumferentially in a counterclockwise direction. The transition passages are offset from adjacent transition passages 30 to induce the zig-zag flow pattern to get the needed pressure drop for inflow control. Flow tests have shown that there are high velocities and inlet passages 12 and 14 as well as at or just past the transition passages 30. While FIGS. 1 and 2 show a single zig-zag movement in the direction of arrow 18 with a transition passage 24 the design can have multiple such generally axially oriented flow arrangements to get the desired pressure drop for a predetermined flow rate. The problem with using such a device or an alternative device shown in FIG. 3 is that there are high velocity regions which cause fluid shearing that if polymer was used through such devices for balancing flow in an injection application, the result would be excessive shear that adversely affects the viscosity of the polymer. It is important to assure that the volume of polymer concentration is maintained and the device is able to effectively balance flow for the polymer phase injection while also balancing flow for different injection fluid phases (i.e. pure water, steam, etc.) that are injected along with or a different times. It has been realized that to effectively inject polymer through a flow balancing device a key design parameter is to reduce high velocity zones that cause shear that adversely affects the viscosity of the polymer that is being injected.
FIG. 3 is another known inflow control device that features a flow inlet 40 leading to an inlet passage 42 followed by a spiral flow pattern to an outlet 44. The velocity at the inlet passage 42 would cause shear affects for the polymer that would adversely affect its viscosity.
What is needed and provided by the present invention is a flow distribution device for polymer injection operation that has a configuration of reducing shear effects on the polymer to minimize adverse effects on its viscosity. Some of the ways this is accomplished is a broad circumferential inlet to a flow path that is circumferentially oriented while providing a zig-zag flow pattern that uses large transition passages to get the zig-zag flow effect which is a design feature enabled by the circumferential orientation of the zig-zag flow. Another way is to introduce the polymer into one or more stacked spiral paths where the entrance to the spiral is a taper that gradually increases polymer velocity and eliminates rapid acceleration approaching the entrance to the spiral. These and other aspects of the device and polymer injection method using the device will be more readily apparent to those skilled in the art from a review of the detailed description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be found in the appended claims.